Master cylinder



-0Ct. 7, 1941. F MA|N MASTER CYLINDER Filed April 18, 1938 2 Sheets-Sheet l INVENTOR FRANK L. MAIN ATTORNEYS Oct. 7, 1941.

F. L. MAIN MASTER CYLINDER I 2 Sheets-Sheet 2 Filed April 18, 1938 INVENTOR FRANK L. MAI N ATTORNEY Patented Oct. 7, 1941 Mesrmecnmlmnt;

Frank; L.- Main; Birmingham; Mich; assignor to Kelsey-Hayes Wheel-:Company, Detroit, Mich, a'corporation oi Delaware. I App i ation nr lq 85193 e ial 110,202 787 TClai ms (01. 60 -5426) escape orzain or other gas from; the sys t em The lo engaging portion 4 of the cylinder flan d prqyid 1 invention has for -other objeots to. so construct the Imalster, cylinder that the pecking' means,.for,, the piston dqes not at anytime enggtge ,aneb'rad ing shoulder, such as formed}, by; a,,port;1 to .so

s he le crl'iders; ough. hat port .,6 The 'mlstonqa in p ti n x d e 0 am1s tr abet/2e :theuppermost part of, thepiston engg. portion.;. The fqrward Q portion ,5 ,fisnadap communicate. with. the r ,tubing leading t wardg portion is ,also adapted to corn nunic with thereservoir through the port ,1 in its upp welL, I

8 isr the ,piston. reoiprgcable; within thewspistqn ith" t e nu ar: rc i am mb r. '2 hi h 18 prefer b yb e n he i ton r danteds. tq-beaclvanc dend t ac dkby means'pf e bellv nk fl ichlisi .connecte to thc istmb he construchthei-master cylinderthatmthe meansJQ armJU anQ; hetconnect n rodnll. The rear e d";

r ing-t m n cation e e ,i hele rr J V0113; and the; cylinder: isscontrolled. by anvalyre sepe-rate from the pistom; amt-to so constructw the master cylinder that," means; commqmto both;

thet l nder .iopensri t h n servqi t. n q ro-ivides clearanceioiathettrm, The connecting fod has the ballgpprtions l2 at its. o pgsite e'n adapted to ,beai; upon lthe piston angll the an the piston and the alye isl adapted to.;.za.ctuatse,"2(MSiiitatlqlejlnihs)l3 connectfthe .ball portionsto the botht The inventionnhas for .further.,objects fllton so construct the masterucylinder that its, parts may the readily for mecl andnssemhledyandeto -50 construct the master v cyl inden-that. the flnctua-r, tionmin the; level of ;the brakinggliqqidm the, reservoiris; greatly reduced andkeptwithin small l limits.

With; these t and other objects; in View the invention nresidesin the novel features oi,cQnst1:1 1'q;-,

as -more fully hereinaftenset forth;

Inthe d aw n s; I Figure .1 is ,a. :plan viewmof a master cylinder. showing an embodiment ofmy invention;

Fi ure 2 a ipntt e eq ipaxtlr section; Fi ure 3 is a c qss.,section nthetl ne ;;o f i u l; Figure 4 is a view,similartojignrefi"shqwing another embodiment .ofjjmy invention;

Figure 5 is a crosslsectiqn on theline 5 -5 qf Figure 4. Re n m i ures ,l, a .1d 3,1 spthema fi l. cylinder which is adapted to deyelop. braking "ag stel'rr, at-ext ndin g w r hdn t a ang .e

' 'pist n and 1 rm,, s1i l c ca ncebein r s ahln, prov ded i or heqpi ns i t h t a l pprfi q s J assure i. contact oithe ballpgrtionswiththeubeag'; H in i ceszo he i tqnn-a id whenthe. r is qnei being-M adi anced. The bell cranks, is, ,preferably eye o he s a t 4 r h qh' e t nd in ransverselyt through the gbody 2 of the, res rvoir; and is 11 journeinits lsi'de wans, "Ihe h ub j of the hel cran' ref erably v tran sversely split, at l 5 a n e e he sca y olt l lsle ,sv m r r k s e or hisya res einsm abl nt-0.,thei rwatdw ort qn; UhQ ri-indert qgo en osi ons he-. y s a n. e:

wit the, "reservoir and, ls lidab ly enga g u b hea-Wanna r ck t 1 9m hat Asui ble q Lsn in i lbetween the.wa11,..ot e

rdrwariporm nlofrnej cylind r; d, he cr -fi h. r

t451 0 czm;2[secured unon; the stem H1 se yes toi brma iyhol iz he Va i H 1 in clq d 1 5 12101 Qt. po it e y en, e valve I e ro qedille. arm 22 upon the bell crank} and. onthe opposite; s ded-the. shaft 4 1mm the arm 1,. his, 3 1 .2

fiuidpressu re int fit p rtion of the brake system lg being engei geqble .with the, up perend of theyglye incl ing he Wheel cyl nd r .t0 pp yihebWk 2S Q of a ,motor vehicle, The master cylinder cornprises the reservoir having the hollow bqd yj and also; comprises the cylinder, 3 formed within and.

"stern when theh'bell. crank, is in itsunorrnal -Qpw he el y nk-1 ada ted tqb r-isw nsfibye means of thelever 23 seo ured uponan enq pf the shaft that one side of; the reservoir the free enq at one sidewof-"the body; AsshoWninlthe. presenti g of this; ==1ever,b ing. connected n by a, linkv toniheu, instance, thecylinderisIormedat the bottompf foot; pedal of the motors vehicle and nhelgl in tr oclp t s: ell wank 1 aveny i v iesl th t 1;

o mal-1 q i brmB Q -O he u ual 1 spring whism connect d t 1t foot p alto. 1 0 C o mal c tismi. zde minethe nmaln q and the adjacent end of the body of the reser- 1,

voir is the flexible diaphragm 21 which is preferably formed of rubber and provides clearance for the bell crank arm Ill and at the same time seals the reservoir from air outside the same, The diaphragm has an inherent resiliency such that as the piston 8 is advanced the diaphragm moves inwardly to substantially compensate for the increased volume of the cylinder in com-, munication with the reservoir to reduce the fluctuationin level of the braking liquid in the reservoir and maintain the level substantially V constant to thereby'prevent surging which tends to fillythe fluid with small air bubbles, The reservoir body is also" provided with the filler neck28having an openupper end through which thebraking liquid-may be poured.

cludedirt, water, etc.

,It.v will be J noted that the port 6 is in axial alignment with the port land the bearing in th'ej'wall' or bracket lfi for the valve stem l8 so that both thejport 1 and the bearing and also the seat for the valve I! may bereadily formed. It will also be noted that by reason of the end cover for the reservoir, the cylinder 3 may be readily machined'and the cooperating parts including the piston, the link, the bell crank, and the} valve retracting spring, readily assembled and secured in,-place, the valve having been inserted-through theport 6. Also the diaphragm and theicover maybereadily secured in place.

.The valve spring 2! is preferably calibrated so..,that a predetermined degree of vacuum in the forward portion 5 of the cylinderduring the retractile movement .of the piston will open the valve 11 ,ther'ebypermitting braking liquid to enter theforward cylinder portion and be added to the braking system. Differently calibrated valve springs may be used to regulate the priming-operation to suit the total leverage employed andjalso to compensate for brake drum expansionjand brake shoe lining wear, so that adjust ment offthe brake shoes to secure a predetermined clearance between the brake drums and linings afterfconsiderable lining wear has occurred need not be urgent or critical. As a result,'it will be seen that priming is not ordinarily a function of piston position, spring tension on the foot pedal, or friction'in the mechanical connections, but is directly controlled by the strength of the valve spring.

,In operation, as the foot pedal is depressed against the tension of the spring holding it in normal position it through the lever 23 and the shaft M. willrnove the bell crank 9 angularly in a counterclockwise direction. During the first portion, oithis movement, the arm 22 of the bell crank" moves away from the valve stem I8 and allows the valve H to close the port I. At the same time, the bell crank arm I through the connecting rod advances the piston 8 andas this advancement continues, the braking liquid is forced outwardly through the port 6 and the tub- 29 is a cap threaded upon the filler neck and forming a' breather to perm'it thepassage of air, but to exing to the wheel cylinders to apply the brakes.

When the foot pedal is released, the parts are returned to their normal positions, the bell crank through the connecting rod retracting the piston. With the valve spring 20 calibrated, the valve will open when a predetermined degree of vacuum occurs in the forward cylinder portion. Also, if the valve is not in open position, the bell crank will positively open the same during the final portion of the retractile movement of the piston. The valve, being open, provides for passage of the braking liquid into the cylinder 3 and also provides for escape of air or other gas from the cylinder 3, or that portion of the brake system beyond the cylinder. In this connection, it is important to note that the master cylinder, I is mounted in a position inclined to the horizontal axis of the vehicle in such a manner that the axis of the cylinder 3 is correspondingly inclined upwardly from its rear end. As a result air or" other gas will not be trapped in the pistonengaging portion of the cylinder.

It will'benoted that the port 1 is'located beyond the limit ofadvance of the piston and its 'packihg ringso thatfneither the piston nor the packing ring can engage'the shoulder formed by the port and be abraded thereby. This is very important, especially with reference to the packing ring.

36 In the modification illustrated in Figures 4 and 5, the construction of the master cylinder in general is the same as that of Figures 1, 2 and 3.

However, the axis of the cylinder is more nearly vertical than horizontal, but the portion "3I of the cylinder forward of the piston engaging portion 32 is, adapted to communicate through the port 33 with the reservoir 34 at a zone elevated aloove'the highest part of the lower end of the piston engaging portion, The 40"construction of master cylinderalso differs in thatthe bell crank 35 is adapted to positively open and close the valve 36, this being accomplished by providing the opposite ends of'the hub s of' the'bell crank with the cam grooves 31 which 4%are engageable by the pins 35 secured to the yoke 39, which in turn is secured to the valve stem 40.

What I claim as my invention is: 7 7 1. A master cylinder, comprising a cylinder, a piston within said cylinder, a reservoir having a portion adapted to communicate with the forward end of said cylinder beyond the limit of advance 7 of said piston, said portion extending to a height above the communication and said cylinder being Minclined downwardly from said portion whereby 4 braking liquid mayflow under gravity from said reservoir into said cylinder and air may pass from said cylinder into said reservoir, a valve controlling the communication, and means op- ;eratively connected to,, said piston and valve to fio advance the piston and to open the valve upon return movement of the piston.

.2.- Amaster cylindencomprising a cylinder, a

vance the piston and open the valve upon return movement of the piston.

3. A master cylinder, comprising a cylinder having a piston engaging portion inclined upwardly toward its forward end and a chamber axially beyond said piston engaging portion, said chamber having a port in its upper side and an outlet in its lower side in alignment with said port, a reservoir extending above said chamber adapted to communicate therewith through said port whereby braking liquid may flow by gravity from said reservoir into said chamber and air may pass from said inclined cylinder into said chamber and through said port into said reservoir, said reservoir having a flange extending inwardly from its forward wall and having an open ing therein in axial alignment with said port and said outlet, a valve for controlling said port having a head extending into said chamber and a stem extending through said port into said reservoir, the upper end of said stem passing through the opening in said flange and extending a predetermined distance above said flange, a spring for normally holding said valve in closed position, a piston reciprocable in said piston engaging portion of the cylinder, and a bell crank having one arm operatively connected to said piston to advance the latter, and another arm engageable with the upper end of said valve stem for opening said valve.

4. A master cylinder, comprising a cylinder having a piston engaging portion. inclined upwardly toward its forward end and a chamber axially beyond said piston engaging portion, said chamber having a port in its upper side and an outlet in its lower side axially beyond said port, said port and said outlet having a common axis inclined upwardly and rearwardly, a reservoir extending above said chamber adapted to communicate therewith through said port whereby braking liquid may flow by gravity from said reservoir into said chamber and air may pass from. said inclined cylinder into said chamber and through said port into said reservoir, said reservoir having a flange extending inwardly from its forward wall and having an opening therein in axial alignment with said port and said outlet, a valve for controlling said port having a head extending into said chamber and a stem extending through said port into said reservoir, the upper end of said stem passing through the opening in said flange and extending a predetermined distance above said fiange, a spring for normally holding said valve in closed position, a piston reciprocable in said piston engaging portion of the cylinder, a shaft extending transversely through said reservoir above said cylinder, a bell crank mounted upon said shaft and having one arm operatively connected to said piston and another arm engageable with the upper end of said valve stem, said bell crank upon rotation in one direction advancing said piston and upon rotation in the other direction opening said valve against the action of said spring, and a stop upon said reservoir engageable with a portion of said bell crank for limiting the movement of said valve by said bell crank.

5. A master cylinder, comprising a cylinder, a piston within said cylinder, a reservoir coinmunicating with the rearward side of the cylinder and having its rearward side open, a cover for the rearward side of the reservoir, said cover having an opening therein, and a diaphragm within said reservoir adjacent the inner surface of said cover for reducing the fluctuation in level of the braking fluid in said reservoir during the reciprocation of said piston.

6. A master cylinder, comprising a cylinder having a piston engaging portion inclined upwardly toward its forward end and having a chamber axially beyond the piston engaging portion, said chamber having a port in its upper side and having an outlet opening in its lower side opposite said port, a reservoir extending above said chamber adapted to communicate therewith through said port whereby braking fluid may flow by gravity from said reservoir into said chamber and air may pass from said inclined cylinder into said chamber and through said port into the reservoir, a valve controlling said port, a piston reciprocable in the piston engaging portion of the cylinder, and means for actuating said valve in timed relation to the movement of the piston.

7. A master cylinder, comprising a cylinder inclined upwardly toward its forward end, a piston within said cylinder, said cylinder having a chamber positioned axially beyond the limit of advance of said piston and having an outlet opening in the lower side of the chamber, a reservoir extending above said chamber adapted to communicate therewith through a port in the upper side of the chamber whereby braking liquid may flow by gravity from the reservoir into the chamber and air may pass from the inclined cylinder into the chamber and through said port into the reservoir, a valve for controlling the port having a head extending into the chamber and having a stem extending through the port into the reservoir, and a member within the reservoir movable in one direction to advance the piston and in the opposite direction to open said valve.

FRANK L, MAIN. 

